In the past there has been a problem of making accurate photometric measurements with laser beams. Problems have occurred because the sensitivity of the detectors utilized for photometric measurements is not constant across the active area of the detector. The detectors have also been direction sensitive. Another problem has been encountered because the energy in the laser beam, particularly in neodymium-YAG laser, is not equally distributed over the cross section of the beam and in that the energy distribution varies rapidly with time. For these reasons, accurate photometric measurements with the laser beam cannot be made either by sampling a part of the beam cross section or by capturing the whole beam within the active area of the detector. Attempts to solve these problems have included the use of a frosted glass diffuser in front of the detector. However, this has not been found to be satisfactory because the coherent nature of the laser beam causes the frosted glass to produce a speckled pattern instead of an evenly distributed beam. Spectrophotometers heretofor provided cannot handle large parts. Also in such devices no provision has been made to compensate for offsets in the beam due to refraction. There is, therefore, a need to provide a laser testing apparatus which overcomes these problems.